Conventionally, mannitol is produced by the catalytic hydrogenation of invert sugar, which is an approximately equimolar mixture of glucose and fructose. Mannitol is produced as a mixture of sorbitol and mannitol in aqueous solution. The yield of mannitol in this situation ranges from 24 to 26% by weight, based on total dry solids, when hydrogenation is carried out under neutral or mildly acidic conditions such as those disclosed in U.S. Pat. No. 2,759,024 by Kasehagen. This yield can be increased by carrying out at least part of the hydrogenation in alkaline conditions, as described in U.S. Pat. Nos. 3,329,729 by Brandner et al. and 3,763,246 to DeBerardinis or by appropriate choice of catalyst, as described in U.S. Pat. No. 3,705,199 to DeBerardinis, or both.
The above processes are plural stage processes in which alkaline hydrogenation is followed by acid hydrogenation. Alkaline agents for the alkaline hydrogenation stages of those processes are alkali metal hydroxides such as sodium hydroxide, and alkaline earth metal hydroxides such as lime. U.S. Pat. No. 3,329,729 also suggests the addition of calcium carbonate as a buffering agent in addition to lime. In the above references, mannitol yeild are as follows: U.S. Pat. No. 3,329,729 is 30 to 36%; No. 3,705,199 is 28 to 29%; No. 3,763,246 is 27 to 31%. In each case, the balance of the reaction product is mostly sorbitol.
U.S. Pat. No. 4,029,578 by Kruse, discloses a process for obtaining sorbitol/mannitol solution from glucose by first catalytically epimerizing glucose in an acidic aqueous solution containing at least 50% by weight of glucose to obtain an epimerizate of glucose and mannose, and then catalytically hydrogenating this epimerizate to obtain an aqueous solution of sorbitol and mannitol. Epimerization according to that process is carried out at elevated temperature in the presence of molybdenum ion, such as molybdic acid or an ion exchange resin in the molybdite form. Hydrogenation catalyst and conditions for hydrogenating the glucose/mannose epimerizate to a mixture of sorbitol and mannitol are known.
Although yields of mannitol can be enhanced by hydrogenating either glucose or invert sugar under alkaline conditions rather than under neutral or mildly acidic conditions, quantities of impurities are also greater when alkaline conditions are used. Thus, there is a need for a hydrogenation process in which enhanced mannitol yield are obtained while minimizing the amounts of impurities.
U.S. Pat. No. 4,292,451 by DeBerardinis discloses a mannitol-rich aqueous solution of sorbitol and mannitol produced by hydrogenating a sugar mixture comprising glucose and mannose in aqueous solution with hydrogen in the presence of a hydrogenation catalyst under hydrogenation conditions. The sugar mixture contains an alkaline metal salt of a weak acid in sufficient quantity so that the percentage of mannitol produced exceeds the percentage of mannitol which would be obtained from hydrogenation of a sugar mixture under non-isomerization conditions. Under the above hydrogenation conditions the percent of mannitol produced is increased to about 40% as compared to about 30 to 35% in cases where no epimerization catalyst is used. Also U.S. Pat. No. 4,083,881 by Takemura et al., discloses a D-glucose solution being epimerized under the conditions of low pH and high temperatures, that is, a pH of 2.0 to 4.5 and temperature of 110.degree. to 160.degree. C., to produce D-mannose at a preferred level ranging from 30 to 36% as compared to 25% which is obtained by the conventional process. Takemura et al also disclose isomerization of the remaining D-glucose in the epimerized mixture of D-fructose with a glucose-isomerase enzyme. This raises the mannose yield to about 46.4% in solution and 40.3% in the crystalline form.
Various attempts have been made to reduce the cost of producing mannitol, such as U.S. Pat. No. 3,677,818 by Casebler et al. which discloses the preparation of substantially pure mannose in the form of a mannose bisulfite adducts from liquor of wood pulping operations which is rich with mannose. This, however, is a very slow process requiring several days to achieve a yield of 24% by weight of the starting material in its crystalline bisulfite adduct form. The mannose bisulfite adduct produced has to be subsequently decomposed to pure mannose in a second time consuming procedure, and the mannose produced is reduced to mannitol.
Another source for mannose is mannan from ivory nut meal which, when hydrolyzed, liberates D-mannose. However, the difficulty of extracting and recovering mannan from this complex natural source in good yield without degrading it has not been commercially feasible. Also, the availability of ivory not meal for use commercially has been limited.
It would be desirable to use mannose or fructose as starting materials to produce mannitol. However, because of the high cost of obtaining mannose or fructose in substantially pure form by the above methods, the economics of using these sugars as starting materials is not justified.
A need has arisen for a low-cost high yield mannitol process. To increase the yield according to the conventional processes would involve starting materials which are too expensive to make such production economically feasible. To satisfy the above need, it has become very desirable to identify a source of mannose or a mannan containing material which would enable easy extraction of mannose or mannan oligomers to be used as starting material for the production of mannitol or other manno-saccharide alcohols.
It has been found that a typical industrial soluble coffee process extraction residue material contains mannan and cellulose. However, its use as a source for mannose or mannan oligomers has not been disclosed. Mainly, coffee extraction residue material has been hydrolyzed to produce galactose (by hydrolyzing its arabinogalactan fraction) or hydrolyzed to produce a random mixture of sugars: galactose, xylose arabinose, mannose and glucose. The hydrolysis of coffee extraction residue material is discussed further and in more details in the following paragraphs.
The process of hydrolyzing extracted coffee grounds is well known in the art. For example, U.S. Pat. No. 2,573,406 to Clough et al. discloses a process for producing a soluble coffee which involves atmospherically extracting about 20% of the weight of the coffee, hydrolyzing a portion of the grounds in a suspension of about 1% sulfuric acid at 100.degree. C. for about 1 hour, adjusting the pH of the hydrolysate, filtering the hydrolysate, combining the same with the atmospheric extract and drying the combined extract. In another, similar process described in U.S. Pat. No. 2,687,355 to Benner et al., phosphoric acid is used in place of sulfuric acid. Still in another process, disclosed in the U.S. Pat. No. 3,224,879 to DiNardo et al. either alkaline or acid hydrolysis is carried out directly in the extraction train of coffee grounds that have been at least atmospherically extracted. Hydrolysis directly in the extraction train eliminates separate hydrolysis step of the prior art processes and provides for adsorption of the alkaline or acid catalyst in the mass of the spent coffee grounds.
As to the Clough et al. and Brenner et al. processes, the batch hydrolysis reactions at relatively low temperatures require about 1 hour to complete, limiting the particularlity of said processes on a commercial scale. Moreover, both Clough et al. and Brenner et al. essentially aim for whatever hydrolysate results from operating at a 100.degree. C. for 1 hour. Neither disclosure describes a method for nor the desirability of manipulating the hydrolysis condition so as to affect the composition of the resulting hydrolyzate. A similar deficiency is noted with respect to the DiNardo disclosure.
It is also widely recognized in the art that cellulosic material containing predominantly carbohydrate polymers and lignins may be hydrolyzed with an acid catalyst at high temperature short time conditions. However, if the cellulosic material is not relatively pure the hydrolysis reaction will produce undesirable by-products. For that reason, the art dealing with acid hydrolysis is of primarily cellulosic material is generally limited to the hydrolysis of waste paper and paper by-product or agricultural waste such as corn hulls, husk or cobs. For example, U.S. Pat. No. 4,201,596 to Church et al. discloses a continuous process for the saccharification of cellulosic material in a tubular reactor with an acid catalyst. The object of the Church et al. process is the conversion to glucose, furfural and xylose of cellulosic waste material such as saw dust, wood waste, corn cob, etc. Along the same line, the kinetics of the conversion of cellulosic waste to monosaccharides in a plug flow reactor are described in Thompson, David R. and Grethlein, James E. "Design Evaluation of a Plug Flow Reactor for a Acid Hydrolysis of Cellulose." Ind. Eng. Chem. Prod. Res. Dev., Vol. 18, No. 3, pp. 166 to 169 (1979). The authors of said article are specifically interested in hydrolyzing cellulose-rich material to monosaccharides essentially glucose. The authors do not disclose a method for hydrolyzing only to oligomers, much less to a specific mix of oligomers. Another disclosure, U.S. Pat. No. 4,316,747 to Rugg et al., describes a process for hydrolyzing cellulosic waste to glucose using an acid catalyst in a twin screw extruder.
Though the art discloses much about the short time high temperature acid hydrolysis cellulose-rich materials, the art does not disclose such treatment of materials in which cellulose is not the major component such as a coffee extraction residue material, particularly the spent coffee grounds from a commercial percolation system. The major hydrolyzable carbohydrate in coffee extraction residue material is mannan. However, in addition to mannan, coffee extraction residue material also contains smaller amounts of carbohydrate polymers such as cellulose and arabinogalactan. The products of mannan hydrolysis degrade under cellulose hydrolysis condition, destroying any desirable mannan oligomer intermediates that are produced.
It is therefore an object of the invention to provide a method of hydrolyzing a coffee extraction residue material to produce manno-saccharides from mannose (DP1) to about manno-decaose (DP10).
Another object of the invention is to provide a method of hydrolyzing a coffee extraction residue material to produce a manno-saccharide made up substantially of mannose.
Still another object of the invention is to neutralize and then reduce the manno-saccharides from the hydrolysis of spent coffee grounds to their corresponding alcohols.
A further object of the invention is to neutralize and reduce the mannose produced to mannitol.
Still a further object of the invention is to produce the alcohols in their powdered or crystalline form.